Method of preparing piezo-electric plates



Nov. 22, 1927.

A. HUND METHOD OF PREPARING PIEZO ELECTRIC PLATES INVENTOR. Yang/Wr M,

Filed Sept. 30. 1925 Patented Nov. 22, 1927.

UNITED STATES PATENT OFFICE?.

AUGUST HUND', 0F BETHESDA, MARYLAND,ASSIGNOR T0 WIRED RADIO, INC., 0FNEW YORK, N. Y., A CORPORATION OF DELAWARE.

'METHOD 0F PREPARING IPIEZO-ELECTRI PLATES.

Application filed September 30, 1925. Serial No. 59,676.

My invention relates broadly to piezo electricity and more particularlyto methods for preparing piezo electric plates for commercial use.

' One of the objects of my invention 1s to provide a method -of grindingpiezo electric plates accurately to a required frequency.

Another object of my invention vis to provide a method of preparing apiezo electric plate by which the frequency of the plate may be comparedwith the. frequency of a standard piezo electric plate and any number ofpiezo electric plates of substantially the same frequency produced.

Still another object of my invention is to provide a visual system forgrinding piezo electric plates to an accuracy within 1/180th kof a cycleand better, even though the desired frequency is of the order of 10ecycles per second or greater.

A further object of my invention is to provide a method of preparingpiezo electric plates by which an audible indication may be obtained ofthe approach of the frequency of the piezo electric plate underpreparation to the frequency of the standard plate with means forvisually observing the final frequency of the plate with respect to thefrequency of the standard plate.

3o Other and further objects of my invention will be understood from thefollowing specification by reference to the accompanying drawings, inwhich z- Figure 1 is a diagrammatic representation of the system which Iemploy for accurately grinding piezo electric plates to the frequency ofa standard piezo electric plateg,i Fig. 2 is a perspective view of thegrinding plate against which the piezo electric plates may be ground forcutting the plate to that thickness which will respond to the desiredfrequency; and Fig. 3 represents a piezo electric plate under treatmentand illustrates in exaggerated form a portion of the plate which isremoved in the grinding process for securing a piezo electric plate' ofdesired frequency characteristics.

Where it is desired to secure oscillations from a piezo electric platewhich are correct for instance within l/180th of a cycle even though thedesired frequency is of vthe order` of 10 cycles per second or more, itis not possible to use the well-known standard frequency meter fordetermination of the frequency of the plate, for frequency meters do nothave the resolving power to indicate such accurate settings. I havediscovered that a beat method lends itself practically in preparing apiezo electric plate having desired frequencies. Piezo electric platesof extremely accurate and predetermined frei quencies are becomingnecessary in the art for the frequency characteristics of a piezoelectric plate possess such constancy that the plates are used for manypurposes. The constant frequency characteristics of piezo electricplates are such that the plates when arranged in properly designedelectrical circuits may beused as a standard of time. A piezo electricpendulum may be provided where-piezo electric plates are arranged tooperate a slow motion indicator producing a beat which may be observedatrecurrin periods of time spaced by time intervals o one second wheredesired. Where the terminals of a communication system are arranged tocooperate with each other on a high frequency channel, it is extremelyimportant that piezo electric plates which are used lto control bothterminals of the system be cut accurately to the same frequency.

Referring more particularly to the drawings, reference characters 1V and2 illustrate electron tubes each having filament, grid and plateelectrodes 1, 1* and 1c, and 2, 2 and 2c, respectively. The electrontubes arel arranged each with separate output circuits 3 and 4 and withindependent input circuits 5 and 6 respectively. In the input circuit ofelectron tube 2 I provide a piezo electric plate 7 of alfstandardfrequency. The standard piezo electric plate is positioned between themetallic plates 8 and 9 and connected in the electron tube circuit by aswitching device 10 which may make contact at 11 or 12 tc position thepiezo electric i plate in sliunt'with the grid and plate electrodes orthe grid and filament electrodes.

of the electron tube system. The cathode 2 is heated from battery 14through rheostat 15. The output circuit of the tube 2 includes thetelephone headset 16, the meter 17 and high potential battery 18 whichare shunted by the radio frequency by-pass condenser 29. A tuned circuitcomprising inductance 2O and variable condenser 19 is connected acrossthe output of the electron standard piezo electric plate 7. In the in.

put circuit of electron tube 1, I connect the piezo electric plate whichis to be accurately ground to the frequency of the standaid piezoelectric plate 7. The piezo electric plate 40 is' initially ground -to athickness in accordance with the formulae which I have set forth in moredetail in the aforementioned application for Letters Patent which willbring the frequency of the plate to within approximately one-half of oneper cent of the required accuracy.

In my aforesaid copcnding application I have determined that thefollowing empirical laws govern the value of the frequency possessed bypiezo electric plates cut in accordance with the principles set forth inthe said application:

pressed in millimeters (mm.)

The piezo electric plate 40 is positioned between metallic plates 41 and42 which are connected between the grid electrode 1l and the switch arm21 arranged to move over contacts 22 and 23 for connecting the plate inshunt with'the grid and plate or grid and filament electrodes. Thecathode heating current is supplied fiom battery 24 under control ofrheostat 25. The output circuit of tube 1 includes telephone receivers26, the indicating meter 27 and high potential battery 28 shunted bycondenser 43 for by-passing radio frequency oscillations. A tuned systemcomprising variable condenser 3() and inductaiice 31 is connected in theoutput circuit of tube l and adjusted to the frequency of the piezoelectric plate 40. A third circuit 44 is coupled with the induct-ances2O and 31 through inductances 33 and 32 respectively, and connected witha rectifier 34, a inilliainmeter 35, and telephone headset 36. Thetelephone headset 36 can indicate audible currents down to about 15cycles per second, while the milliainmeter 35 can show alternatingcurrent variationsl between zero and fifteen cycles. IVhere the piezoelectric plate 40 is cut approximately to the required thickness thefrequency thereof is lower than the frequency of the stand ard piezoelectric plate 7. This will give rise to a beat frequency in circuit 44which will give an audible indication intelephone headset 36 and avisual indication in the meter 35 in `accordance with the expression:

f1=fiiifn where f1 is the frequency of the iezo electric plate 40 whichis to be groun to the frequency of the standard piezo electric plate 7.fn represents the frequency of the standard piezo electric plate 7 andfB is the beat frequency in circuit 44. -The piezo electric plate 40should be cut a triiie over-size so that f1 is somewhat smaller than fu.rlhe difference in frequency between the plate 40 and the plate 7 willbe observed both audibly in telephone headset 36 and visually by meansof the meter 35. Where the difference is large the plate 40 is removedfrom its position between metallic plates 41 and 42 and passed over agrinding plate 37. The grinding plate 37 is provided with laterally andlongitudinally extending grooves 38 and 39 which provide cutting facesbetween which a. mixture of emery powder and water is provided. Theplate 4() is returned to its position between the metallic plates 41 and42 and a lower beat note is observed in the circuit 44. 'Ihis beat notemay approach closer and closer to fifteen cycles and then pass beyondaural ability to hear a tone in the telephone headset 36. The process ofgrinding is repeated until the visual beat indicator 35 nioves to andfro. Three to and fro niotions per second show that the frequency of theplate 40 is 0H by three cycles per second and one to and fro motion inone minute indicates that the beat frequency is off by 1/60th of acycle. This process of grindingextremely narrow surface cuts from thecrystal 40 is carried on until a complete Zero beat effect is obtained.In Fig. 3 I have represented the piezo electric plate 40 as having anoriginal thickness A and a final thickness B when the proper' frequencyis obtained, but it will be realized that the difference in thicknesswhich has been represented in the drawings has been greatly exaggeratedfor the normal grinding operation of the piezo electric plate againstthe grinding surface 37 consists in passing the piezo electric platelightly over the grinding surface to remove an infinitesimal thicknessof the surface of the plate. I may employ a modified method of fixingthe frequency of a piezo electric plate with respect to a standard witha high degree of precision.

The necessity for piezo electric plates of exactly the saine frequencycharacteristics will be more fully appreciated when their application tocarrier wave signaling systems is considered. In these systems it isoften desirable to suppress the carrier' frequency from transmission.The carrier frequency however must be renewed or restored at thereceiving station so that piezo electric plates the same temperature toavoid any errors quency is ters 'Patent of which might occur due totemperature differences. Appropriate means maybe provided formaintaining the temperature of each plate constant. i f

While I have described my invention in certain preferred embodiments, Idesire that.

it be understood that modifications may be made and that I intend nolimitations upon the invention other than those imposed by thescope ofthe appendedclaims.

What I claim and desire to secure by Letthe United States is asfollows 1. In an apparatus for the preparation of 'A piezo electricplates for the generation of predetermined frequencies, the combinationof a pair of oscillatory circuits, a standard frequency piezo electricplate arranged to control the frequency of one of said oscillatorycircuits, a piezo electric plate whose freto be fixed arranged tocontrol said other oscillator circuit, said last, mentioned plate havingan initial thickness corresponding to a frequency lower than thefrequency of said standard plate, and an intermediate circuit coupledwith each of said oscillator circuits -and having means therein forindicating the difference between the frequencies of said standard piezoelectric plate and said piezo electric plate whose frequency is to befixed, said last mentioned piezo electric plate being capable of areduction in thickness to the required dimension for the generation ofoscillations equal in frequency to the oscillatlons generated by saidstandard piezo elec- 'tric plate. y

2. In a system'for preparing piezo electric plates of predeterminedfrequency, the combination ofa pair of oscillatory circuits, one of saidcircuits being controlled by a standard piezoelectric plate of knownfrequency and the other of said oscillatory circuits being controlled bya piezo electric plate whose frequency is to be' fixed. said lastmentioned plate having an initial thickness correspond-l ing to afrequency lower than the frequency of said standard plate, a thirdcircuit coupled to said oscillatory circuits. and lneans in said thirdcircuitfor indicating the difference in frequency between said piezoelectric plates, said last Vmentioned piezo electric plate being capableof. a reduction to a thickness yatiwhich oscillations equal in frequencyvmentioned plate having an initiall thickness to the oscillationsgenerated' byvsaid standard piezo electric plate are produced.v

3. In a system for preparing piezo electric plates of predeterminedfrequency thev combination of a pair of oscillatory circuits, one ofsaid circuits being controlled by a standard piezo electric plate ofknown frequency and the other of said oscillatory circuits beingrcontrolled by a piezo.. electric plate whose frequency is to be fixed,said last corresponding to a frequenc lower than the frequency of saidstandar plate, a third circuit coupled with each of said oscillatorycircuits, and meansconnected in said third circuit for both audibly andvisually indicating the difference between the frequency of said lastmentioned piezo electric plate and said standard piezo electric plate,said` last mentioned piezo electric plate being capable of a dimensionalreduction to a thickness at wlii'choscillations equal in frequency tothe oscillations of said standard piezo electric plate are produced.

. 4. In an apparatus for preparing piezo electric plates the combinationof apar o oscillatory circuits, one of said circuits being controlled bya standard piezo electric plate of `known frequen and the other of saidcircuits being contro ed by a piezo eleco5 tric plate whose frequency isto be determined, said last mentioned plate having an initial thicknesscorrespondingA to a frequency lower than the frequency of said standardplate, a third circuit coupled vto each of said oscillator circuits,rectifying mean-s con- A nected in said third circuit, and visual andaudible indicating means connected with said rectifying means, saidaudible indicating means being arranged to indicate, the dii'er- 105ence in frequency between said standard piezo electric plate and saidlast mentioned piezo lelectric plate through a given frequency range,and said visual indicating means being arranged to indicate thedifference in frequency below the audible frequency range between saidgiven frequency limit and zero, said la-st mentioned piezo electricplate being capable of a reduction to a thickness at which oscillationsof a frequency correspending to the frequency of the oscillations ofsaid standard piezo electric plate may be produced.

5. A piezo electric apparatus comprising4 in combination adfpair ofoscillatory circuits,

a standard piezo electric plate of known frequency arranged tofcontrolone of said os- .cillatory circuits, a piezo electric plate of slightlydifferent frequency arranged to control said other oscillatory circuit,a third circuit coupled with each of said oscillatory circuits andhaving means therein for indicating the difference in frequency betweensaid piezo electric plates.

`6. In a..p1ezo` electric apparatus the cem- 13? bnation of apair ofelectron tubes each having grid, filament and plate electrodes, inputand output circuits for each of said tubes. interconnecting saidelectrodes, a standard piezo electric plate of known frequency arrangedto be connected between the filament and grid 01` between the plate andgrid of one of said electron tubes` a second piezo electric plate ot'slightly different lfrequency arranged to be connected between thefilament and grid 0r between the plate and grid of said other electrontube for impressing upon each of said output circuits constant frequencyoscillations of slightly different frequencies and a third circuitcoupled with In testimony whereof I atix my signa- 20 ture.

AUGUST HUND.

